The universal mobile telecommunications system (UMTS) is a third-generation mobile communications system evolving from the global system for mobile communications system (GSM), which is the European standard. The UMTS is aimed at providing enhanced mobile communications services based on the GSM core network and wideband code-division multiple-access (W-CDMA) technologies.
A UMTS network structure 1 is illustrated in FIG. 1. As shown, a mobile terminal, or user equipment (UE) 2 is connected to a core network (CN) 4 through a UMTS terrestrial radio access network (UTRAN) 6. The UTRAN 6 configures, maintains and manages a radio access bearer for communications between the UE 2 and the core network 4 to meet end-to-end quality of service requirements.
The UTRAN 6 includes a plurality of radio network subsystems (RNS) 8, each of which comprises one radio network controller (RNC) 10 for plurality base stations, or Node Bs 12. The RNC 10 connected to a given base station 12 is the controlling RNC for allocating and managing the common resources provided for any number of UEs 2 operating in one cell. One or more cells exist in one Node B. The controlling RNC 10 controls traffic load, cell congestion, and the acceptance of new radio links. Each Node B 12 may receive an uplink signal from a UE 2 and may transmit a downlink signals to the UE 2. Each Node B 12 serves as an access point enabling a UE 2 to connect to the UTRAN 6, while an RNC 10 serves as an access point for connecting the corresponding Node Bs to the core network 4.
Among the radio network subsystems 8 of the UTRAN 6, the serving RNC 10 is the RNC managing dedicated radio resources for the provision of services to a specific UE 2 and is the access point to the core network 4 for data transfer to the specific UE. All other RNCs 10 connected to the UE 2 are drift RNCs, such that there is only one serving RNC connecting the UE to the core network 4 via the UTRAN 6. The drift RNCs 10 facilitate the routing of user data and allocate codes as common resources.
The interface between the UE 2 and the UTRAN 6 is realized through a radio interface protocol established in accordance with radio access network specifications describing a physical layer (L1), a data link layer (L2) and a network layer (L3) described in, for example 3GPP specifications. These layers are based on the lower three layers of an open system interconnection (OSI) model that is a well-known in communications systems.
An architecture of the radio interface protocol is illustrated in FIG. 2. As shown, the radio interface protocol is divided horizontally into the physical layer, the data link layer, and the network layer, and is divided vertically into a user plane for carrying data traffic such as voice signals and Internet protocol packet transmissions and a control plane for carrying control information for the maintenance and management of the interface.
The physical layer (PHY) provides information transfer service to a higher layer and is linked via transport channels to a medium access control (MAC) layer. Data travels between the MAC layer and the physical layer via a transport channel. Also, data transmission is performed through a physical channel between different physical layers, namely, between physical layers of a sending side (transmitter) and a receiving side (transmitter).
The MAC layer of the second layer (L2) provides information transfer service to a higher layer and is linked via a logical channel to a radio link control (RLC) layer. The RLC layer of the second layer (L2) supports the transmission of reliable data and can perform segmentation and concatenation functions for RLC service data units (SDU) received from an upper layer.
The radio resource control (RRC) layer located at the lowest portion of the third layer (L3) is only defined in the control plane and controls transport channels and physical channels with respect to the establishment, re-establishment, and release of radio bearers. A radio bearer (RB) is a service provided by a lower layer, such as the RLC layer or the MAC layer, for transferring data between the UE 2 and the UTRAN 6.
The establishment of an RB determines regulating characteristics of the protocol layer and channel needed to provide a specific service, thereby establishing the parameters and operational methods of the service. When a connection is established to allow transmission between an RRC layer of a specific UE 2 and an RRC layer of the UTRAN 6, the UE 2 is said to be in the RRC-connected state. Without such connection, the UE 2 is in an idle state.
Hereafter, a Multimedia Broadcast/Multicast Service (MBMS or “MBMS service”) will be described. MBMS refers to a method of providing streaming or background services to a plurality of UEs 2 using a downlink-dedicated MBMS radio bearer that utilizes at least one of a point-to-multipoint radio bearer and a point-to-point radio bearer. One MBMS service includes one or more sessions and MBMS data is transmitted to the plurality of terminals (i.e. UEs) through the MBMS radio bearer only while the session is ongoing.
A MBMS may be carried out in a broadcast mode or a multicast mode. The broadcast mode is for transmitting multimedia data to all UEs 2 within a broadcast area, for example the region where the broadcast is available. The multicast mode is for transmitting multimedia data to a specific UE 2 group within a multicast area, for example the region where the multicast service is available.
The UTRAN 6 provides the MBMS service to the UEs 2 using the RB. RBs used by the UTRAN 6 can be classified as a point-to-point RB or a point-to-multipoint RB. The point-to-point RB is a bi-directional RB, including a logical channel DTCH (Dedicated Traffic Channel), a transport channel DCH (Dedicated Channel) and a physical channel DPCH (Dedicated Physical Channel) or SCCPCH (Secondary Common Control Physical Channel).
The point-to-multipoint RB is a uni-directional downlink RB, including a logical channel MTCH (MBMS Traffic Channel), a transport channel FACH (Forward Access Channel), and the physical channel SCCPCH, as shown in FIG. 3. The logical channel MTCH is configured for each MBMS service provided to one cell and used to transmit user plane data of a specific MBMS service to multiple UEs.
FIG. 3 is a diagram for explaining channel mapping for MBMS. Referring to FIG. 3, a point-to-multipoint radio bearer includes a logical channel MTCH (MBMS traffic channel), a transport channel FACH (forward access channel) and a physical channel SCCPCH. The logical channel MTCH is configured for each MBMS offered by one cell and is used in transmitting user-plane data of a MBMS to a plurality of UEs.
A logical channel MCCH (MBMS control channel), as shown in FIG. 3, is a point-to-multipoint downlink channel and is used in transmitting control information associated with the MBMS. The logical channel MCCH is mapped to the transport channel FACH (forward access channel), while the transport channel FACH is mapped to the physical channel SCCPCH (secondary common control physical channel). One cell has one MCCH.
FIG. 4 is a conceptual view illustrating a transmission method of the MCCH information. The MCCH information is periodically transmitted according to a modification period and a repetition period. The MCCH information is divided into critical information and non-critical information. Among the critical information and non-critical information, the non-critical information may be modified at a modification period or a repetition period. However, the modification of the critical information may be made only at a modification period. Therefore, the critical information is repeated once during each repetition period in order to be transmitted. However, the transmission of the modified critical information may only occur at a start point of a modification period.
The MCCH information includes one or more control messages (i.e., RRC message, MBMS Modified Services Information (MSI), MBMS Unmodified Services Information (USI), MBMS point-to-multipoint radio bearer information and access information, etc) of the MBMS. Among these messages, the access information is considered as non-critical information, and any other MCCH information messages are considered as critical information.
The access information is used to operate a counting process. Based on the access information, the UE executes a RRC connection process, cell update process, or URA update process by transmitting a counting process response message, such like a RRC connection request message, cell update message, or URA update message.
As the UTRAN transmits all the messages, a message is sent with a MBMS transmission identity if that message has information about a particular service. Here, the MBMS transmission identity is formed with a MBMS Session Identity and a MBMS Service Identity. For example, when the MSI needs to be transmitted, the MSI contains the MBMS Session Identity together with service information which is represented by the MBMS Service Identity.
The UTRAN periodically transmits a physical channel MICH (MBMS notification indicator channel) to indicate whether the MCCH information was updated during the modification period. Therefore, a UE attempting to receive only a certain MBMS does not receive the MCCH or MTCH until a session of the certain MBMS service begins. However, the UE does receive a MICH (MBMS notification indicator channel) periodically. An update of the MCCH information is referring to the generation, addition, modification and/or removal of a specific item of the MCCH information.
Also, the UTRAN periodically transmits the MSI message with the physical channel MICH to indicate whether the MCCH information was updated. The MSI message contains identity information of all service(s) which were updated in a current cell during the modification period and required operating information for a service subscribed UE. Here, the MBMS Transmission Identity is used for the identity information. The MBMS Transmission Identity is consisted of a MBMS service identity which indicates a specific service or the MBMS Transmission Identity is consisted of a MBMS service identity with the MBMS Session Identity which indicates a specific session of specific service. From current services provided in the cell, the identity information of the unmodified service during the modification period is transmitted via a USI message. In this case, the MBMS Transmission Identity is used for the identity information of such service.
Once a session of a specific MBMS begins, the UTRAN transmits an NI (notification indicator). The NI is an indicator that provides notification to receive an MCCH to a UE attempting to receive a specific MBMS. Upon receiving the NI via the MICH, the UE receives an MCCH during a specific modification period indicated by the MICH. During a reception of the MCCH, the UE initially receives the MSI message to determine whether the MBMS service desired by the UE during the modification period, is updated or not, then receives a modified MCCH information if an update exists. The UE can find out all service lists provided from the current cell by receiving a transmitted MSI message and USI message within the modification period.
Therefore, the UE wanting to receive the specific MBMS using the point-to-multipoint RB, receives the MCCH information including the RB information via the MCCH, and establishes the point-to-multipoint RB using the MCCH information. After establishing the point-to-multipoint RB, the UE continuously receives the physical channel SCCPCH, to which the MTCH is mapped, to obtain data of the specific MBMS transmitted via the MTCH.
The UTRAN can transmit MBMS data discontinuously via the MTCH. In this case, as illustrated in FIG. 3, the UTRAN periodically transmits a scheduling message to the UE through a MBMS Scheduling Channel (MSCH) of SSCPCH which the MTCH is mapped. The scheduling message notifies a transmission start time point and a transmission duration for the MBMS data which is transmitted during one scheduling period. In order to perform this, the UTRAN has to inform a transmission period of scheduling information to the UE in advance.